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File::Find(3pm) Perl Programmers Reference Guide File::Find(3pm)
NAME
File::Find - Traverse a directory tree.
SYNOPSIS
use File::Find;
find(\&wanted, @directories_to_search);
sub wanted { ... }
use File::Find;
finddepth(\&wanted, @directories_to_search);
sub wanted { ... }
use File::Find;
find({ wanted => \&process, follow => 1 }, ’.’);
DESCRIPTION
These are functions for searching through directory trees doing work on each file
found similar to the Unix find command. File::Find exports two functions, "find"
and "finddepth". They work similarly but have subtle differences.
find
find(\&wanted, @directories);
find(\%options, @directories);
"find()" does a depth-first search over the given @directories in the order
they are given. For each file or directory found, it calls the &wanted subrou-
tine. (See below for details on how to use the &wanted function). Addition-
ally, for each directory found, it will "chdir()" into that directory and con-
tinue the search, invoking the &wanted function on each file or subdirectory in
the directory.
finddepth
finddepth(\&wanted, @directories);
finddepth(\%options, @directories);
"finddepth()" works just like "find()" except that is invokes the &wanted func-
tion for a directory after invoking it for the directory’s contents. It does a
postorder traversal instead of a preorder traversal, working from the bottom of
the directory tree up where "find()" works from the top of the tree down.
%options
The first argument to "find()" is either a code reference to your &wanted function,
or a hash reference describing the operations to be performed for each file. The
code reference is described in "The wanted function" below.
Here are the possible keys for the hash:
"wanted"
The value should be a code reference. This code reference is described in "The
wanted function" below.
"bydepth"
Reports the name of a directory only AFTER all its entries have been reported.
Entry point "finddepth()" is a shortcut for specifying "<{ bydepth =" 1 }>> in
the first argument of "find()".
"preprocess"
The value should be a code reference. This code reference is used to preprocess
the current directory. The name of the currently processed directory is in
$File::Find::dir. Your preprocessing function is called after "readdir()", but
before the loop that calls the "wanted()" function. It is called with a list of
strings (actually file/directory names) and is expected to return a list of
strings. The code can be used to sort the file/directory names alphabetically,
numerically, or to filter out directory entries based on their name alone. When
follow or follow_fast are in effect, "preprocess" is a no-op.
"postprocess"
The value should be a code reference. It is invoked just before leaving the cur-
rently processed directory. It is called in void context with no arguments. The
name of the current directory is in $File::Find::dir. This hook is handy for
summarizing a directory, such as calculating its disk usage. When follow or fol-
low_fast are in effect, "postprocess" is a no-op.
"follow"
Causes symbolic links to be followed. Since directory trees with symbolic links
(followed) may contain files more than once and may even have cycles, a hash has
to be built up with an entry for each file. This might be expensive both in
space and time for a large directory tree. See follow_fast and follow_skip
below. If either follow or follow_fast is in effect:
* It is guaranteed that an lstat has been called before the user’s
"wanted()" function is called. This enables fast file checks involving _.
* There is a variable $File::Find::fullname which holds the absolute path-
name of the file with all symbolic links resolved
"follow_fast"
This is similar to follow except that it may report some files more than once.
It does detect cycles, however. Since only symbolic links have to be hashed,
this is much cheaper both in space and time. If processing a file more than
once (by the user’s "wanted()" function) is worse than just taking time, the
option follow should be used.
"follow_skip"
"follow_skip==1", which is the default, causes all files which are neither
directories nor symbolic links to be ignored if they are about to be processed a
second time. If a directory or a symbolic link are about to be processed a sec-
ond time, File::Find dies.
"follow_skip==0" causes File::Find to die if any file is about to be processed a
second time.
"follow_skip==2" causes File::Find to ignore any duplicate files and directories
but to proceed normally otherwise.
"dangling_symlinks"
If true and a code reference, will be called with the symbolic link name and the
directory it lives in as arguments. Otherwise, if true and warnings are on,
warning "symbolic_link_name is a dangling symbolic link\n" will be issued. If
false, the dangling symbolic link will be silently ignored.
"no_chdir"
Does not "chdir()" to each directory as it recurses. The "wanted()" function
will need to be aware of this, of course. In this case, $_ will be the same as
$File::Find::name.
"untaint"
If find is used in taint-mode (-T command line switch or if EUID != UID or if
EGID != GID) then internally directory names have to be untainted before they
can be chdir’ed to. Therefore they are checked against a regular expression
untaint_pattern. Note that all names passed to the user’s wanted() function are
still tainted. If this option is used while not in taint-mode, "untaint" is a
no-op.
"untaint_pattern"
See above. This should be set using the "qr" quoting operator. The default is
set to "qr│^([-+@\w./]+)$│". Note that the parentheses are vital.
"untaint_skip"
If set, a directory which fails the untaint_pattern is skipped, including all
its sub-directories. The default is to ’die’ in such a case.
The wanted function
The "wanted()" function does whatever verifications you want on each file and
directory. Note that despite its name, the "wanted()" function is a generic call-
back function, and does not tell File::Find if a file is "wanted" or not. In fact,
its return value is ignored.
The wanted function takes no arguments but rather does its work through a collec-
tion of variables.
$File::Find::dir is the current directory name,
$_ is the current filename within that directory
$File::Find::name is the complete pathname to the file.
Don’t modify these variables.
For example, when examining the file /some/path/foo.ext you will have:
$File::Find::dir = /some/path/
$_ = foo.ext
$File::Find::name = /some/path/foo.ext
You are chdir()’d to$File::Find::dir when the function is called, unless "no_chdir"
was specified. Note that when changing to directories is in effect the root direc-
tory (/) is a somewhat special case inasmuch as the concatenation of
$File::Find::dir, ’/’ and $_ is not literally equal to $File::Find::name. The table
below summarizes all variants:
$File::Find::name $File::Find::dir $_
default / / .
no_chdir=>0 /etc / etc
/etc/x /etc x
no_chdir=>1 / / /
/etc / /etc
/etc/x /etc /etc/x
When <follow> or <follow_fast> are in effect, there is also a $File::Find::full-
name. The function may set $File::Find::prune to prune the tree unless "bydepth"
was specified. Unless "follow" or "follow_fast" is specified, for compatibility
reasons (find.pl, find2perl) there are in addition the following globals available:
$File::Find::topdir, $File::Find::topdev, $File::Find::topino, $File::Find::topmode
and $File::Find::topnlink.
This library is useful for the "find2perl" tool, which when fed,
find2perl / -name .nfs\* -mtime +7 \
-exec rm -f {} \; -o -fstype nfs -prune
produces something like:
sub wanted {
/^\.nfs.*\z/s &&
(($dev, $ino, $mode, $nlink, $uid, $gid) = lstat($_)) &&
int(-M _) > 7 &&
unlink($_)
││
($nlink ││ (($dev, $ino, $mode, $nlink, $uid, $gid) = lstat($_))) &&
$dev < 0 &&
($File::Find::prune = 1);
}
Notice the "_" in the above "int(-M _)": the "_" is a magical filehandle that
caches the information from the preceding "stat()", "lstat()", or filetest.
Here’s another interesting wanted function. It will find all symbolic links that
don’t resolve:
sub wanted {
-l && !-e && print "bogus link: $File::Find::name\n";
}
See also the script "pfind" on CPAN for a nice application of this module.
WARNINGS
If you run your program with the "-w" switch, or if you use the "warnings" pragma,
File::Find will report warnings for several weird situations. You can disable these
warnings by putting the statement
no warnings ’File::Find’;
in the appropriate scope. See perllexwarn for more info about lexical warnings.
CAVEAT
$dont_use_nlink
You can set the variable $File::Find::dont_use_nlink to 1, if you want to force
File::Find to always stat directories. This was used for file systems that do not
have an "nlink" count matching the number of sub-directories. Examples are
ISO-9660 (CD-ROM), AFS, HPFS (OS/2 file system), FAT (DOS file system) and a cou-
ple of others.
You shouldn’t need to set this variable, since File::Find should now detect such
file systems on-the-fly and switch itself to using stat. This works even for
parts of your file system, like a mounted CD-ROM.
If you do set $File::Find::dont_use_nlink to 1, you will notice slow-downs.
symlinks
Be aware that the option to follow symbolic links can be dangerous. Depending on
the structure of the directory tree (including symbolic links to directories) you
might traverse a given (physical) directory more than once (only if "follow_fast"
is in effect). Furthermore, deleting or changing files in a symbolically linked
directory might cause very unpleasant surprises, since you delete or change files
in an unknown directory.
NOTES
· Mac OS (Classic) users should note a few differences:
· The path separator is ’:’, not ’/’, and the current directory is denoted as
’:’, not ’.’. You should be careful about specifying relative pathnames.
While a full path always begins with a volume name, a relative pathname
should always begin with a ’:’. If specifying a volume name only, a trail-
ing ’:’ is required.
· $File::Find::dir is guaranteed to end with a ’:’. If $_ contains the name
of a directory, that name may or may not end with a ’:’. Likewise,
$File::Find::name, which contains the complete pathname to that directory,
and $File::Find::fullname, which holds the absolute pathname of that direc-
tory with all symbolic links resolved, may or may not end with a ’:’.
· The default "untaint_pattern" (see above) on Mac OS is set to "qr│^(.+)$│".
Note that the parentheses are vital.
· The invisible system file "Icon\015" is ignored. While this file may appear
in every directory, there are some more invisible system files on every
volume, which are all located at the volume root level (i.e. "Macin-
toshHD:"). These system files are not excluded automatically. Your filter
may use the following code to recognize invisible files or directories
(requires Mac::Files):
use Mac::Files;
# invisible() -- returns 1 if file/directory is invisible,
# 0 if it’s visible or undef if an error occurred
sub invisible($) {
my $file = shift;
my ($fileCat, $fileInfo);
my $invisible_flag = 1 << 14;
if ( $fileCat = FSpGetCatInfo($file) ) {
if ($fileInfo = $fileCat->ioFlFndrInfo() ) {
return (($fileInfo->fdFlags & $invisible_flag) && 1);
}
}
return undef;
}
Generally, invisible files are system files, unless an odd application
decides to use invisible files for its own purposes. To distinguish such
files from system files, you have to look at the type and creator file
attributes. The MacPerl built-in functions "GetFileInfo(FILE)" and "Set-
FileInfo(CREATOR, TYPE, FILES)" offer access to these attributes (see
MacPerl.pm for details).
Files that appear on the desktop actually reside in an (hidden) directory
named "Desktop Folder" on the particular disk volume. Note that, although
all desktop files appear to be on the same "virtual" desktop, each disk
volume actually maintains its own "Desktop Folder" directory.
BUGS AND CAVEATS
Despite the name of the "finddepth()" function, both "find()" and "finddepth()"
perform a depth-first search of the directory hierarchy.
HISTORY
File::Find used to produce incorrect results if called recursively. During the
development of perl 5.8 this bug was fixed. The first fixed version of File::Find
was 1.01.
perl v5.8.6 2001-09-21 File::Find(3pm)
Generated by $Id: phpMan.php,v 4.55 2007/09/05 04:42:51 chedong Exp $ Author: Che Dong
On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
2008-11-22 08:02 @38.103.63.58 CrawledBy CCBot/1.0 (+http://www.commoncrawl.org/bot.html)